The most detailed online material on the details of this language I could find: Raganswamy Jagannathan, Chris Dodd. GLU programmer's guide (downloadable as the 4th paper of GIPSY Publications). The first pages seem to discuss other problems, but it is worth of reading further, because a detailed description of Lucid's syntax and semantics is hiding inside this paper (section 3.1.2 on pages 22--38). This paper is part of the Gipsy Project Home Page (GIPSY: A General Intensional Programming System).

written to mimick and test the following Lucid example (I have made it a little Haskell-like -- it is not original Lucid syntax, but it is not an embedding into Haskell language, either -- in fact, it is a didactic intermediate syntax):

In fact, first, next, fby are not necessarily primitives in Lucid, but this fast-food implementation treats them as primitives.

The above example may suggest that Lucid be necessarily synchronous -- it reacts on inputs in a one-output-for-each-input way. This is not the case: Lucid has general, unrestricted stream processing abilities (thus able to implement also asynchronous processes).